This is just a quick introduction to the basic functions of any camera and to give you a little understanding of some of the terms commonly used. For many of you this will be like teaching granny to suck eggs, but for others, having the relationships between speed, aperture and depth of field explained in simple terms might be helpful when you take the camera out of automatic.

Shutter Speed

This is simply the amount of time that the camera shutter is open and allowing light to fall on the sensor. The faster the shutter opens and closes, the less light is allowed to fall on the sensor. The time is usually measured in fractions of a second such as 1/125th or 1/250th. Generally a shutter speed of longer than 1/60th of a second will result in blurred photographs due to hand-shake or subject movement.

Aperture

Aperture refers to the size of the opening inside a lens that allows light through the lens and onto the sensor. This is often referred to as the ‘F stop’ or ‘F number’ such as F8 or F16. The larger the number, the smaller the opening. There is an obvious relationship between the shutter speed and the aperture. For any given light conditions, if you reduce the time that the shutter is open (to catch a fast moving object clearly for example) then you will need to increase the size of the opening in the lens by selecting a lower F number. Conversely, if you decrease the size of the opening by selecting a higher F number (for reasons I’ll come onto) then you must increase the time that the shutter is open, allowing more light to fall onto the sensor. Aperture also has a direct influence on depth of field that I’ll come to shortly.

Put practically, if you take a picture and it is too dark overall, you could select a smaller F number giving a larger opening in the lens (aperture) to allow in more light, OR you could use a longer shutter speed to give more time for the available light to reach the sensor.

Depth of Field

In simple terms, depth of field describes how much of an image will be in focus in terms of range, ie: from back to front of the photograph. Your depth of field is potentially determined by three things.

1. The primary effect on depth of field is the aperture you are using; a small aperture (High F stop) will give you a large depth of field. This would be useful for landscapes for example.

A large aperture (Low F stop) will give you a shallow depth of field. This might be useful for portrait photography where you want a blurred back ground.

2. The size (or focal length) of your lens; the higher the magnification of your lens, the shallower the depth of field. For example, take a lens with a focal length range of 70mm to 200mm zoom lens photographing the same subject from the same position and with the same aperture. At low magnification (70mm) you may have a large depth of field. As you increase the magnification up to 200mm, the depth of field will shallow accordingly.

3. The distance from your subject; in simple terms, the closer you are to your subject, the more shallow your depth of field will be.

These three factor can all work together. For instance, if you used a large aperture (Low F Number), zoomed in (High Magnification) on a close subject, you would have a tiny depth of field. If you moved further back from the subject or reduced magnification, so you depth of field would increase. You can thus play with your depth of field in these three ways to make a face stand out from the blurred background for instance.

Next time I’ll look at how we might use the relationships between speed, aperture and depth of field I’ve described above to help get the pictures we want in different situations. If you liked this article or have any questions then feel free to comment below. If you feel you want to know more and would like to have a one-on-one with us then contact us here

Ian Weaver

Remember, I am trying to approach these subjects in layman's terms, but I do have an expert photographer on hand to firstly check these blogs for accuracy, and to answer any questions that I personally cannot field.